The present invention relates to an asymmetrically exciting type magnetic device made of composite magnetic materials capable of generating a steep pulse electromotive force in response to the action of an exterior magnetic field.
The exterior magnetic field can be produced by a permanent electromagnet or the magnetic field induced when an electric current flows.
Such electromagnetic type pulse generators are adapted to be used to produce the pulse signals for the position of a moving body and can be applied to electric and electronic apparatuses and automatic control systems all of which need a large number of successive pulse signals.
In addition, they can be used as an operation timing control device with a high accuracy for generating pulse signals for controlling various computers in an automotive vehicle and ensuring an optimum ignition operation of a gasoline engine and an optimum heating or cooling operation in response to the variations in gas pressure in a stirling engine.
The present invention can be also used as an ampere meter and a current sensor for detecting an overcurrent in an electric distribution system.
The electric current sensor can be used to detect not only the current including a direct current which ranges from a super low frequency range to a high frequency range but also to measure an overcurrent such as an impulse.
The present invention further provides measuring instruments which can be used in voltage meters and ampere meters.
Furthermore, the magnetic device in accordance with the present invention can be widely used as a special magnetic storage device for writing and reading information under the action of an exterior magnetic field.
Various methods for producing pulses by utilizing electromagnetic induction have been used and demonstrated.
In general, the magnitude of the electromotive force produced by the electromagnetic induction is dependent upon the variations in time of the magnetic flux intersecting a detection coil mounted on a ferromagnetic material so that when the variation ratio becomes extremely low, no electromotive force is produced.
However, extensive studies and experiments have been conducted to find magnetic materials, which are not dependent upon the ratio of variations in time of the intersecting magnetic flux. For instance, according to a Bistable Magnetic Device disclosed in U.S. Pat. No. 3,820,090 by J. R. Wiegand, a Self-Nucleating Magnetic Wire is produced by subjecting permalloy to a tension and twisting process so that the coercive force at the shell portion is stronger than that at the core portion. It has a phenomenon that when one exterior magnetic field disappears, a pulse is generated and that when the magnetic field disappears, the direction of magnetization of the core portion of the wire establishes a return magnetic path of the shell by self reversal. Therefore the underlying principle of the above-mentioned wire is that in response to the variations of the magnetic flux, a pulse is generated across a detection coil.
The above-described reversal phenomenon inevitably occurs when the external magnetic field disappears because in the case of a short magnetic body, the action of the opposite magnetic field at each pole is generally dominant. However, the output pulse thus produced is relatively low and there is a defect that it is very difficult to correctly control a time point at which a pulse is generated.
So far, as means for indirectly measuring the value of a current flowing through a line, there has been used a method in which the magnetic field produced when the current flows through the line is trapped by an instrumental transformer utilizing iron cores, but this method has also the problem that the magnetic circuit and the winding cannot be made compact in size and light in weight.
Furthermore, there has been proposed and used a method in which an electric current is measured by a semiconductor element utilizing the Hall effect and a magnetic circuit, but this method also has the problem that the temperature characteristic and stable operation cannot be ensured so that this method is not reliable in operation.
The utilization of composite magnets especially as a current sensor has been proposed and demonstrated, but this method has the problems that the detection capability is remarkably varied depending upon the magnetization history, i.e. how the composite magnetic body used was previously magnetized. This is an inevitable phenomenon depending upon the magnetic hysteresis so that when used as an electric current sensor, it must be provided with some suitable correction means.
On the other hand, according to the present invention, an asymmetric excitation type composite magnetic body is used so that various objects of the present invention can be attained by a simple means.
An ignition device in accordance with the present invention can be used not only in a conventional contact type ignition system but also a non-contact ignition system which has been developed recently.
At present, there are known electromagnetic type pickups for generating pulse signals equal to the number of the gear shaped magnetic poles per rotation of the rotating shaft of a distributor.
In this case, when the diameter of the gear-shaped magnetic pole is, for instance, of the order of 30 mm, the upper limit of the angle of rotation for generating one pulse is of the order of from 10.degree. to 15.degree. so that there has been a strong demand for a pulse generator capable of generating pulses at a high degree of resolution of the order of 1.degree. or less.
Furthermore, the conventional ignition systems need at least two kinds of signals each representative of the angle of rotation of the crankshaft.
More particularly, one kind of pulse is needed to control the angle of rotation of the above-mentioned distributor while the other kind of pulse is needed to detect which cylinder is operated or ignited.
In order to generate such two kinds of pulse signals, two signal generators are mounted and must be spaced apart from each other by a suitable distance to prevent mutual electromagnetic induction interference. It follows therefore that the whole volume of the two signal generators inevitably becomes large so that there has been also a demand for signal generators compact in size and light in weight or just one generator capable of accomplishing the functions of two signal generators.
Furthermore, in the case of the storage devices utilizing the conventional magnetic bodies, in order to increase the output voltage derived on the read-out operation, means for increasing the ratio of variations of the intersecting magnetic flux have been provided. As a result, there exist the problems that the electric current for generating the magnetic field must be shaped in the form of a rectangular waveform and that the magnetic body must be rotated at a high speed.